Fairing for a combustion chamber end wall

[0028]FIG. 1 shows an example of a turbojet in half-section on a section plane containing the axis of rotation X of the turbojet rotor. The turbojet comprises a centrifugal high-pressure compressor (not shown), and downstream therefrom a diffuser 4 opening out into a space 5 defined between concentric outer and inner casings 6 and 7, and occupied by an annular combustion chamber 8 supported by the casings 6 and 7.

[0029]Although FIG. 1 relates to a turbojet with a centrifugal compressor, the invention is not limited to this type of turbomachine.

[0030]The combustion chamber 8 has an inner 2 wall, an outer wall 3, and, in the upstream region of said chamber, an annular end wall 11 disposed between said inner and outer walls. This end wall 11 presents inner and outer fastener rims 11a and 11b folded upstream relative to the main portion of the end wall 11.

[0031]The end wall 11 carries injector heads 12 forming part of a system 13 for feeding fuel via fuel injectors 14 passing through the space 5. These elements shown in FIG. 1 are not reproduced on the other figures.

[0032]The combustion chamber 8 is fitted with an annular fairing 10. The fairing 10 covers the end wall 11 to protect it, and presents openings 16 for passing said injectors 14. The section of the fairing 10 in the plane of FIG. 1 is substantially semicircular in shape. Thus, the fairing 10 presents good stiffness and therefore better dynamic behavior than the behavior of prior art “cowl” fairings. It is also suitably aerodynamically contoured.

[0033]In addition, in accordance with the invention, the fairing 10 is subdivided into a plurality of adjacent sectors referenced 100, 100′ (see FIGS. 2 to 5) or 200, 200′, 200″ (see FIG. 6). In this example, the adjacent sectors are all identical, which enables them to be mass produced.

[0034]Naturally, the number of sectors can vary. Thus, for a combustion chamber 8 having eighteen fuel injectors 14, fitted with a fairing 10 presenting one opening 16 for each injector 14, i.e. eighteen openings, it is possible for example to subdivide the fairing into eighteen sectors, each sector presenting a single opening 16, or indeed to subdivide a fairing into nine, six, or even three sectors, each sector then presenting respectively two, three, or six openings 16. Naturally, the smaller the number of sectors, the quicker the fairings 10 can be assembled, but the smaller the flexibility of the sectors. Conversely, the greater the number of sectors, the more flexible they are and the easier it is to obtain good contact between the fastening edges of these sectors and the outer and inner walls 3 and 2, but the longer it takes to assemble the fairing 10. Furthermore, the greater the number of sectors, the better vibration is damped.

[0035]In general, each fairing sector presents at least one opening allowing at least one fuel injector to pass therethrough. FIGS. 2 to 5 show embodiments in which each sector 100, 100′ presents a single opening 16 allowing one fuel injector 14 to pass therethrough. FIG. 6 shows an embodiment in which each sector 200, 200′, 200″ presents three openings16, each opening serving to pass one fuel injector 14. In other embodiments (not shown), each fairing sector presents one or more openings, each opening extending far enough circumferentially to allow a plurality of fuel injectors to pass therethrough.

[0036]With reference to FIGS. 2 to 5, each sector 100 overlies the upstream side of the chamber end wall 11 and has inner and outer fastener edges 100a and 100b that are fastened to the inner and outer fastener rims 11a and 11b of the chamber end wall 11, and to the upstream edges 2a and 2b of the inner and outer walls 2 and 3 at various fastening points. More precisely, the outer fastener edge 100b (or the inner edge 100a) of the fairing sector, the upstream edge 3b (or 2a) of the outer wall 3 (or inner wall 2), and the outer fastener rim 11b (or inner rim 11a) of the chamber end wall 11 are superposed from the outside towards the inside of the combustion chamber 8, and they have holes passing therethrough that coincide with one another and that receive bolts 15. The bolts 15 hold said edges 100a, 100b, 3a, 3b, and rims 11a, 11b assembled to one another and they are distributed around two concentric circles around the axis X.

[0037]Each of the adjacent sectors 100 and 100′ in FIGS. 2 to 5 present two side edges 101, 102 and 101′, 102′, and when these sectors are assembled together, the side edge 101 of the sector overlies the side edge 102′ of the adjacent sector 100′. Thus, there are no circumferential gaps between the assembled-together sectors, thus making it possible to limit or even eliminate any leakage of air between the sectors.

[0038]More particularly, in the embodiment in the figures, each sector 100 has a lip 105 at its side edge 101 that is connected to the remainder of the sector by a step 107. This lip 105 overlaps the side edge 102′ of the adjacent sector 100′ when the sectors 100 and 100′ are assembled together (see FIGS. 2, 4, and 5). The step 107 can also as an abutment for the side edge 102′ of the sector 100′, thus making it easier to put the sectors into place relative to one another.

[0039]In the embodiments of FIGS. 2 to 4, the inner and outer fastener edges 100a and 100b of each sector 100 are each fastened at two fastening points. These two fastening points are situated respectively at the side edges 101 and 102 of the sector 100. More precisely, these two fastening points are implemented by means of a bolt 15 passed through a hole 108 or 109 passing through the corresponding fastener edge. At least one of said holes is oblong, its long dimension being oriented in the circumferential direction of the fairing 10. The oblong hole 100 allows the bolt 15 to move towards and away from each other, where such movement can be caused either during mounting of the sector 100 on the walls 2 and 3, or else in operation as a result of differences in expansion between the sector 100 and the walls 2, 3, and/or 11 of the chamber 8. This avoids stresses appearing in the sector 100.

[0040]In the embodiment of FIGS. 2 to 4, two circular holes 109 are formed respectively in the fastener edges 100a and 100b beside the side edge 102, while two oblong holes 108 are formed respectively in the fastener edges 100a and 100b beside the side wall 101. More precisely, the two oblong holes 108 pass through the lip 105.

[0041]FIG. 5 is a view analogous to that of FIG. 4 showing two adjacent sectors 100, 100′ of another embodiment of a fairing of the invention. The fairing sectors 100, 100′ in FIG. 5 differ from those in FIG. 4 solely concerning their fastening points with the chamber end wall. In the embodiment of FIG. 5, the inner and outer fastener edges 100a and 100b of each sector 100 are each fastened at a single fastening point. This fastening is provided by a bolt 15 passed through a hole 111 that passes through the fastener edge 100a or 100b of the sector. This minimizes the number of bolts 15 and of holes 111, thereby minimizing the weight and the cost of fabricating the sector 100.

[0042]Advantageously, said fastener point is situated outside the overlap zone between sectors 100, but is positioned close to said zone. In this way, part of the clamping force of the bolt 15 is used to cause the side edge 101 of the sector 100 to exert pressure on the side edge 102′ of the adjacent sector 100′ and to hold the sector 100′ in position.

[0043]The fairing 10 of FIG. 5 can be assembled as follows: firstly the sector 100 is fastened to the chamber end wall 11, without fully tightening the bolts 15 passing through the openings 111, and then the side edge 102′ of the adjacent sector 100′ is passed under the lip 105. Thereafter, the second sector 100′ is fastened without fully tightening the bolts 15 passing through the openings 111′, so as to enable the side edge of another adjacent sector (not shown) to be passed under the lip 105′ of the sector 100′, and so on. Once all of the sectors are in place, the bolts 15 are fully tightened.

[0044]It should be observed that because the sectors overlap, the first sector 100, when fastened partially only (e.g. by the bolt 15 not being fully tightened), holds the second sector 100 before it is bolted to the chamber end wall. This makes it easier to mount the fairing sectors.